The Polarized Hydrogen Gas Jet Target. From RHIC to EIC.

The Polarized Hydrogen Gas Jet Target Polarimeter (HJET) at the Relativistic Heavy-Ion Collider (RHIC) is employed for the precise measurement of absolute transverse (vertical) polarization of proton beams, achieving low systematic uncertainties of approximately σˢystP/P ≤ 0.5%. Extensive studies have evaluated HJET performance, including measurements of the pp and pA analyzing powers over a broad range of proton and ion beam energies (4--250 GeV/nucleon). These findings support the proposition of employing HJET for proton and ³He beams polarimetry at the future Electron-Ion Collider (EIC) with a required accuracy of 1%. In this review, we discuss the HJET data analysis methods used at RHIC, emphasizing their relevance for the EIC. Additionally, suggestions are presented for enhancing HJET performance to reliably meet the specific polarimetry requirements of the EIC.